In many conventional mobile networks, a mobile terminal is assigned a dedicated channel for its uplink (and downlink) data transmissions. For example, in a pure FDMA (Frequency Division Multiple Access) system, the terminal is assigned a dedicated frequency channel and in a pure TDMA (Time Division Multiple Access) systems, the terminal is assigned a dedicated time slot. In CDMA (Code Division Multiple Access) networks, there is no dedicated channel, but one transmission carrier frequency (often shortly referred to as ‘carrier’ hereinafter) is provided which serves multiple terminals, i.e. each of multiple mobile terminals transmits data on one and the same carrier. CDMA systems up to W (Wideband)-CDMA networks of 3GPP (3rd Generation Partnership Project) release are based on the single-carrier approach. However, the next generation of CDMA networks will be multi-carrier networks in which a mobile terminal may transmit (and receive) data on several carrier frequencies in parallel. In other words, in such multi-carrier-networks there may be several mobile terminals per carrier and several carriers per mobile terminal.
In a single-carrier CDMA system, the network controls the transmissions of a terminal in downlink and in uplink direction. With regard to the control of uplink transmissions, the network issues access grants indicating a particular (maximum) data rate, which the mobile terminal may use on the uplink carrier. The network determines the grant based on data transmission requests from the terminals and an interference between the ongoing transmissions on the uplink carrier. For example, the so-called “happy bit” approach comprises setting a 1-bit flag in uplink control messages indicating to the network whether or not the terminal is happy with the current grant. A terminal will request a higher data rate in case the current data in its transmission buffer cannot be emptied (within a predetermined time) with the currently granted data rate. Basically, in a single-carrier CDMA system, the interference headroom is shared between the multiple terminals transmitting in parallel and by issuing the same amount of grants to those mobile terminals that have (more) data to transmit, i.e. which are unhappy, the interference headroom is shared in a fair way.
However, applying the above simple approach to a multi-carrier system does not lead to an optimal usage of transmission resources neither from the point of view of the network (i.e. on a radio interface) nor from the point of view of a single terminal. For example, a simple happy bit approach cannot avoid that too many mobile terminals select the same carrier for their transmissions, which causes high interference on this carrier, while other carriers remain unused. Therefore, some control is required of how the mobile terminals select carriers for transmission. Such a control technique should provide for an optimized usage of the available transmission resources from a network point of view, i.e. on a radio interface. Further it should provide for an optimized usage of the available transmission resources from a terminal point of view, i.e. the transmission data throughput should be maximized which includes the requirements of optimal usage of the available transmission power and minimized interference (maximized robustness) on the used carriers. Moreover, the control technique should lead to optimum results in very different circumstances regarding the widely varying possible transmission requirements of multiple terminals on multiple transmission carriers.